1. Field of the Invention
The present invention relates to a microwave plasma processing device which processes an object to be processed by generating plasma using a microwave and a gate valve for the microwave plasma processing device.
2. Description of the Related Art
For example, in a semiconductor device manufacturing process, microwave plasma processing devices which perform predetermined processing by generating plasma using a microwave and causing this plasma to act on an object to be processed have been conventionally used. As one of these microwave plasma processing devices, the one that continuously performs processing while carrying the object to be processed by a belt conveyor or the like under atmospheric pressure has been known. It has been known that such a microwave plasma processing device is provided with a microwave leakage preventing structure to prevent leakage of plasma from a plasma head portion which generates the plasma by a microwave to its surroundings (for example, see JP-A 2005-32805).
On the other hand, in a microwave plasma processing device which performs predetermined processing by housing an object to be processed in a processing chamber and generating plasma under a vacuum atmosphere, the inside of the processing chamber needs to be hermetically sealed. Therefore, an opening to carry the object to be processed in and out is openably and closably sealed with a valve element of a gate valve or the like, and thereby the inside of the processing chamber is hermetically isolated from the outside thereof during plasma processing.
In the above conventional microwave plasma processing device which performs the plasma processing under the vacuum atmosphere, for example, in a portion where members constituting the processing chamber are fixed while being brought into contact with each other, leakage of the microwave to the outside is prevented, for example, by putting a spirally formed member called a spiral shield between these members.
However, as a result of a detailed investigation of the present inventor et al., it turns out that the conventional microwave plasma processing device with the above structure has the following problem. Namely, when the plasma processing is performed with the plasma in a steady state, the microwave is absorbed by the plasma, so that the microwave never leaks to the outside of the processing chamber. However, when there is no plasma, for example, when the plasma is ignited, there is a possibility that the microwave spreads over respective portions inside the processing chamber, from a slight gap between the valve element formed in the gate valve portion and a processing chamber wall, is transmitted through a hermetically blocking member (so-called O-ring or the like) made of resin or the like and leaks to the outside of the processing chamber. In some cases, this leaked microwave causes an undesired electric discharge, for example, in a transfer chamber or the like placed adjacent to the processing chamber.
When such microwave leakage as described above is prevented, a structure in which the valve element and the processing chamber are brought into direct contact with each other and no gap is formed therebetween is conceivable. However, in the case of the above structure in which the valve element and the processing chamber are brought into direct contact, the metal valve element and the metal processing chamber come into direct contact at every opening/closing operation of the valve element, so that a possibility that so-called particles occurs increases, and a possibility that the object to be processed is badly influenced increases. Hence, the above structure is undesirable in terms of suppression of the occurrence of the particles.